The present invention concerns a friction joint for fixing a first machine element to a second machine element, said friction joint being established with the aid of at least one sleeve-like member so that said sleeve-like member has been disposed around said first machine element, and that said second machine element has been disposed to receive said sleeve-like element.
For integral joining between a shaft and a hub, a keyway and a simple uniform key have long been applied. As a consequence of better materials and more accurate manufacturing procedures, a friction joint of this type is too coarse nowadays.
The following characteristics, among others, are required of ideal tightenable joints. The shaft and the central hub hole must be completely cylindrical. The tolerances and surface quality requirements of the force-transmitting joint must be reasonable. The joint must retain the original centering. It must be possible to separate and reestablish the joint several times. Axial displacement of the joint should be easy to accomplish. Establishing of the joint should not require the use of special tools. The direction of torque (driving vs. driven) must be changeable in a force-transmitting joint. The friction joint should not necessitate the use of securing keys and the like, whereby economy in shaft thickness becomes possible.
The characteristics listed above are not achievable with a conventional key joint, and the key joint is therefore a rather unsatisfactory solution.
For the purpose of establishing a friction joint, the so-called ETP sleeve has recently been developed, by the aid of which it is possible to mount on a shaft elements such as sprocket wheels, belt pulleys, gear wheels, clutches, cams, flywheels, rolls, levers, cutting disks, etc. A sleeve of this type replaces the conventional joint constructions previously applied, such as keyways, rifling, splining, set screws, welded, cone, tightening and crimp joints, etc. The ETP sleeve expands against the two surfaces which are meant to transmit the torque. This expansion is achieved by means of a pressure fluid applied between the inner and outer walls of the sleeve. The pressure fluid is acted upon by a pressure ring, which is tightened by means of common hex head screws. Although by this design a number of remarkable advantages are gained, its greatest drawback are its scaling problems. It is also a fact that the ETP sleeve comprises a great number of components and this solution is therefore comparatively complex.